Move direct struct recursion check to detect recursion in global structs.

test/libsolidity/syntaxTests/structs/recursion/recursive_struct_forward_reference.sol

@@ -4,7 +4,7 @@ contract C {
     function f(Data.S memory a) public {}
 }
 contract Data {
-    struct S { S x; }
+    struct S { S[] x; }
 }
 // ----
 // TypeError: (63-78): Recursive type not allowed for public or external contract functions.

test/libsolidity/syntaxTests/structs/struct_var_member.sol

@@ -0,0 +1,7 @@
+contract C {
+	struct S {
+		var x;
+	}
+}
+// ----
+// ParserError: (27-30): Expected explicit type name.

test/libsolidity/syntaxTests/types/global_struct_recursive.sol

@@ -0,0 +1,8 @@
+struct s1 { s2 x; }
+struct s2 { s1 y; }
+
+contract C {
+    // whatever
+}
+// ----
+// TypeError: (0-19): Recursive struct definition.